diff --git a/.gitignore b/.gitignore
index 0f3420a..fdf6837 100644
--- a/.gitignore
+++ b/.gitignore
@@ -133,3 +133,5 @@ dmypy.json
 
 # Pyre type checker
 .pyre/
+
+.DS_Store
\ No newline at end of file
diff --git a/src/autometrics/prometheus_url.py b/src/autometrics/prometheus_url.py
index 614add6..96e4bbd 100644
--- a/src/autometrics/prometheus_url.py
+++ b/src/autometrics/prometheus_url.py
@@ -4,13 +4,17 @@
 
 
 class Generator:
-    def __init__(self, functionName, moduleName):
+    def __init__(self, functionName, moduleName, baseUrl=None):
         load_dotenv()
         self.functionName = functionName
         self.moduleName = moduleName
-        self.baseUrl = os.getenv("PROMETHEUS_URL")
+        self.baseUrl = baseUrl or os.getenv("PROMETHEUS_URL")
         if self.baseUrl is None:
-            self.baseUrl = "http://localhost:9090/"
+            self.baseUrl = "http://localhost:9090"
+        elif self.baseUrl[-1] == "/":
+            self.baseUrl = self.baseUrl[
+                :-1
+            ]  # Remove the trailing slash if there is one
 
     def createURLs(self):
         requestRateQuery = f'sum by (function, module) (rate (function_calls_count_total{{function="{self.functionName}",module="{self.moduleName}"}}[5m]))'
@@ -30,5 +34,5 @@ def createURLs(self):
 
     def createPrometheusUrl(self, query):
         urlEncode = urllib.parse.quote(query)
-        url = f"{self.baseUrl}graph?g0.expr={urlEncode}&g0.tab=0"
+        url = f"{self.baseUrl}/graph?g0.expr={urlEncode}&g0.tab=0"
         return url
diff --git a/src/test_prometheus_url.py b/src/test_prometheus_url.py
new file mode 100644
index 0000000..d9b7f65
--- /dev/null
+++ b/src/test_prometheus_url.py
@@ -0,0 +1,34 @@
+import unittest
+from autometrics.prometheus_url import Generator
+
+
+# Defaults to localhost:9090
+class TestPrometheusUrlGeneratorDefault(unittest.TestCase):
+    def setUp(self):
+        self.generator = Generator("myFunction", "myModule")
+
+    def test_createPrometheusUrl(self):
+        url = self.generator.createPrometheusUrl("myQuery")
+        self.assertTrue(
+            url.startswith("http://localhost:9090/graph?g0.expr=")
+        )  # Make sure the base URL is correct
+        self.assertIn("myQuery", url)  # Make sure the query is included in the URL
+
+
+# Creates proper urls when given a custom base URL
+class TestPrometheusUrlGeneratorCustomUrl(unittest.TestCase):
+    def setUp(self):
+        self.generator = Generator(
+            "myFunction", "myModule", baseUrl="http://localhost:9091"
+        )
+
+    def test_createPrometheusUrl(self):
+        url = self.generator.createPrometheusUrl("myQuery")
+        self.assertTrue(
+            url.startswith("http://localhost:9091/graph?g0.expr=")
+        )  # Make sure the base URL is correct
+        self.assertIn("myQuery", url)  # Make sure the query is included in the URL
+
+
+if __name__ == "__main__":
+    unittest.main()